Noncontact acoustic manipulation using a standing wave field in air

Abstract

A noncontact manipulation technique is necessary to develop micro-machine technology, biotechnology, and new materials processing. The authors have developed an acoustic manipulation technique to transport particles in water [T. Kozuka, Proceedings of WCU2003, Paris, 483–486 (2003)]. Although it is more difficult to generate a strong sound field in air than in a liquid, many researchers are actively studying the trapping of particles, droplets, and aerosols in air using ultrasound. Nevertheless, many of the resultant studies only trap and observe objects; they do not transport them. This paper describes an advanced manipulation technique to transport small objects in air using that scheme. A standing-wave field was generated by two sound beams (40 kHz) using bolted Langevin transducers. The beams’ axes cross each other. Expanded polystyrene chips were trapped at nodes of the sound pressure in the crossing sound beams. The trapped position was shifted by changing the phase difference of the two sound beams. In addition, transportation at constant speed of the trapped target was realized by a slight difference in ultrasonic frequency between the two sound beams. This system is also applicable to liquid droplets and aerosols in air.